I’m 20 now and I have 1 unit and I co-manage a portfolio.

. - You can get more units in the City of Detroit, but you will need to understand the City's demographics or you'll get taken advantage of.City of Detroit has 183+ residential Neighborhoods.

Apartment noises - neighbors sounds (flushing bathrooms from other units, sirens from street, etc.) 

You could potentially put as little as 3% down if it's a single family home and 5% down for 2-4 units.

I want to be able to find potential markets/listings nationally based on the return.

@Ken M. rents are softening in the places that have had a lot of new units come on line.  

Also, sometimes they travel with their family so it may be beneficial to rent it out by the unit and not by the room. 

You said that you are applying for an FHA loan so it sounds as though you'd be living in one unit. 

It's probably not going to end well for that landlord.We actually had this happen to us twice last year (at the same time, in 2 different units)!

As you look to scale, just make sure to hold/build reserves for when repairs come up and take your time screening tenants as you will find a vacant unit is much less stressful than dealing with a bad tenant.